Needles Of Trees Research Articles

Photosynthetic Characteristics of Eastern Dwarf Mistletoe (Arceuthobium pusillum Peck) and its Effects on the Needles of Host White Spruce (Picea glauca [Moench] Voss)

Abstract: We studied the biochemical composition and photosynthetic characteristics of the aerial parasite eastern dwarf mistletoe (Arceuthobium pusillum) and the effect of infection on the needles of host white spruce (Picea glauca) in a coastal forest stand in Maine, USA. Eastern dwarf mistletoe was capable of photosynthetic oxygen evolution; however, rates were low and were exceeded by respiratory oxygen consumption at all light intensities through full sunlight. Therefore, eastern dwarf mistletoe acts as a net sink for host photosynthate. Relative to those of uninfected trees, needles from infected branches of white spruce were significantly smaller in terms of length, fresh weight, maximum cross section and the diameter of the vascular cylinder. Needles of uninfected and infected trees did not differ in terms of fresh weight to dry weight ratio, nor in nitrogen, soluble sugar or starch content. Needles of infected trees possessed significantly less α‐carotene and neoxanthin, but did not otherwise differ from uninfected needles in terms of chlorophyll and carotenoid composition. Since specific physiological roles for α‐carotene and neoxanthin have not been described, the functional significance of the decreases in their content is not known. Photosynthetic capacities of needles from infected and uninfected white spruce did not differ significantly, as measured by oxygen evolution. These findings suggest that dwarf mistletoe infection does not substantially perturb host white spruce source‐sink balance at the end of the growing season and that carbon exchange dynamics between the host and parasite are unlikely to fully explain the detrimental effects of infection on white spruce.

Stomatal conductance alone does not explain the decline in foliar photosynthetic rates with increasing tree age and size in Picea abies and Pinus sylvestris

Foliar light-saturated net assimilation rates (A) generally decrease with increasing tree height (H) and tree age (Y), but it is unclear whether the decline in A is attributable to size- and age-related modifications in foliage morphology (needle dry mass per unit projected area; M(A)), nitrogen concentration, stomatal conductance to water vapor (G), or biochemical foliage potentials for photosynthesis (maximum carboxylase activity of Rubisco; V(cmax)). I studied the influences of H and Y on foliage structure and function in a data set consisting of 114 published studies reporting observations on more than 200 specimens of various height and age of Picea abies (L.) Karst. and Pinus sylvestris L. In this data set, foliar nitrogen concentrations were independent of H and Y, but net assimilation rates per unit needle dry mass (A(M)) decreased strongly with increasing H and Y. Although M(A) scaled positively with H and Y, net assimilation rates per unit area (A(A) = M(A) x A(M)) were strongly and negatively related to H, indicating that the structural adjustment of needles did not compensate for the decline in mass-based needle photosynthetic rates. A relevant determinant of tree height- and age-dependent modifications of A was the decrease in G. This led to lower needle intercellular CO2 concentrations and thereby to lower efficiency with which the biochemical photosynthetic apparatus functioned. However, V(cmax) per unit needle dry mass and area strongly decreased with increasing H, indicating that foliar photosynthetic potentials were lower in larger trees at a common intercellular CO2 concentration. Given the constancy of foliar nitrogen concentrations, but the large decline in apparent V(cmax) with tree size and age, I hypothesize that the decline in Vcmax results from increasing diffusive resistances between the needle intercellular air space and carboxylation sites in chloroplasts. Increased diffusive limitations may be the inevitable consequence of morphological adaptation (changes in M(A) and needle density) to greater water stress in needles of larger trees. Foliage structural and physiological variables were nonlinearly related to H and Y, possibly because of hyperbolic decreases in shoot hydraulic conductances with increasing tree height and age. Although H and Y were correlated, foliar characteristics were generally more strongly related to H than to Y, suggesting that increases in height rather than age are responsible for declines in foliar net assimilation capacities.

Tree- and needle-age-dependent variations in antioxidants and photoprotective pigments in Norway spruce needles at the alpine timberline.

To cope with environmental stress, plants are equipped with antioxidative (e.g., ascorbate, glutathione and alpha-tocopherol) and photoprotective (e.g., xanthophyll cycle pigments) defense systems. We investigated the defense capacities of three tree age classes (mature, sapling and seedling) of Norway spruce (Picea abies (L.) Karst.) at a field site near the timberline. Biochemical data were expressed on both a needle dry mass and a surface area basis. Compared with current-year needles, previous-year needles contained higher mass- and area-based concentrations of chlorophylls and alpha-tocopherol, and a larger xanthophyll cycle pool that was in a more epoxidized state. Total glutathione concentration was lower, the glutathione pool was more reduced and the ascorbate pool was more oxidized in previous-year needles than in current-year needles. Needle concentrations of glutathione and alpha-tocopherol increased and chlorophyll concentration decreased with increasing tree age when expressed on a surface area basis. On a dry mass basis, these trends were reversed or nonexistent. The ascorbate pool was more reduced and the glutathione pool was more oxidized in needles of mature trees than in needles of saplings and seedlings. The proportion of protective xanthophyll cycle pigments decreased and the de-epoxidation state increased with increasing tree age. We conclude that tree age and the basis of expression of antioxidant concentration--surface area or dry mass--are important in scaling from seedlings to large trees.

Minimum cuticular conductance and cuticle features of Picea abies and Pinus cembra needles along an altitudinal gradient in the Dolomites (NE Italian Alps).

Winter desiccation is believed to contribute to stress in coniferous trees growing at the treeline because cuticular conductance increases with altitude. To test whether winter desiccation occurs in high-altitude conifers of the Dolomites (NE Italian Alps), we measured minimum cuticular conductance (g(min)), needle wettability (contact angle) and cuticle thickness in Picea abies (L.) Karst. and Pinus cembra L. needles from December to August. Samples were collected from adult trees along an altitudinal gradient from valley bottom (1050 m a.s.l.) to the treeline (2170 m a.s.l.). The treeline site is one of the highest in the area and is characterized by a generally low wind exposure. Altitude had no effect on g(min) in either species. In P. abies, large seasonal variations in g(min) were recorded but no changes were related to needle age class. Pinus cembra had a low g(min) and appeared to be efficient in reducing needle water losses. There was a significant increase in g(min) with needle aging in P. cembra growing at low altitude that could be related to a shorter needle longevity compared with P. abies. High contact angles (> 110-120 ) suggested the presence of tubular epicuticular waxes on needles of both species. Contact angles were higher (low wettability) in high-altitude needles than in low-altitude needles. By the end of winter, there was no difference in contact angles between needles in the windward and leeward positions. Wax structures transformed toward planar shapes as demonstrated by the decrease in contact angle from winter to summer. In both species, the cuticle was thicker in needles of high-altitude trees than in needles of low-altitude trees and there was no correlation between g(min) and cuticle thickness. Because desiccation resistance did not decrease with altitude in either species, we conclude that they are not susceptible to winter desiccation at the tree line.

Physiological study of declining Pinus cembra (L.) trees in southern France

Pinus cembra (L.) trees growing at an elevation of 1,800 m in the Mercantour Alps National Park in southern France have shown various degrees of damage (yellowing and needle loss) since the early 1980s. Two stands were selected, one populated by healthy and the other by damaged trees, and 1-year-old needles were analysed. The needles of the declining trees displayed chlorotic mottled patterns associated with a significantly lower level of total chlorophyll compared to healthy trees. Measurements of gas exchange showed a lower photosynthetic rate linked to a lower activity of ribulose bisphosphate carboxylase and a higher stomatal conductance in needles of declining trees compared to healthy trees. In contrast, phosphoenolpyruvate carboxylase activity was found to be higher in declining tree needles, reaching twice the level measured in healthy tree needles. A significant oxidative stress was also observed in the needles which presented a 68% higher malondialdehyde content than healthy tree needles. The atmospheric concentration of ozone was quite high (40 nl·l–1, monthly mean in summer) in both stands but preliminary results based on stomatal conductance and ozone concentration measurements suggested a higher ozone flux in needles of declining trees. Ozone is thus suspected as a contributing factor in the observed decline of Pinus cembra trees.

Needle anatomy changes with increasing tree age in Douglas-fir.

Morphological differences between old-growth trees and saplings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) may extend to differences in needle anatomy. We used microscopy with image analysis to compare and quantify anatomical parameters in cross sections of previous-year needles of old-growth Douglas-fir trees and saplings at the Wind River Canopy Crane site in Washington and at three sites in the Cascade Mountains of Oregon. We also compared needle anatomy across a chronosequence of 10-, 20-, 40- and 450-year-old Douglas-fir trees from the Wind River site. Anatomy differed significantly between needles of old-growth trees and saplings at all sites, suggesting a developmental change in needle anatomy with increasing tree age. Compared with needles of old-growth trees, needles of saplings were longer and had proportionately smaller vascular cylinders, larger resin canals and few hypodermal cells. Astrosclereids, which sequester lignin in their secondary cell walls and occupy space otherwise filled by photosynthetic cells, were scarce in needles of saplings but abundant in needles of old-growth trees. Needles of old-growth trees had an average of 11% less photosynthetic mesophyll area than needles of saplings. The percentage of non-photosynthetic area in needles increased significantly with increasing tree age from the chronosequence of 10-, 20-, 40- and 450-year-old trees at the Wind River site. This reduction in photosynthetic area may contribute to decreased growth rates in old trees.

Soil properties under a Pinus radiata - ryegrass silvopastoral system in New Zealand. Part I. Soil N and moisture availability, soil C, and tree growth

Understanding the changes in soil properties in silvopastoral systems is important in regulating the interactions between tree and understorey pastures. In this study, the effects of understorey management on soil mineral N and moisture availability, soil temperature, soil C, and tree growth were investigated in a seven-year-old silvopastoral agroforestry experiment in Canterbury, New Zealand. The systems included understorey treatments of bare ground and ryegrass (Lolium perenne) pasture. Soil mineral N, moisture content, and temperature were monitored from July 1997 to July 1998 in two positions (0.9 and 3.5 m north of tree rows) and two soil depths (0–10 and 10–20 cm). Soil C and N in the 0–10 cm depth were higher in the ryegrass than in the bare ground plots, reflecting the organic C and N input in the ryegrass plots, as well as greater N loss from the bare ground plots in the form of nitrate leaching and/or denitrification. Soil C was higher in the position 0.9 m than 3.5 m away from the tree rows, possibly caused by the greater C input from decomposing fine tree roots and needle litterfall at the 0.9 m position. Soil moisture availability was greater in the bare ground than in the ryegrass plots in the summer. No effect of understorey management on soil temperature was found. Soil nitrate levels were lower in the ryegrass plots and may be limiting when soil moisture supply was adequate. Tree volume growth from winter 1997 to 1998 was significantly greater in the bare ground treatment, reflecting better soil moisture and N supply conditions.

Polychlorinated biphenyls and organochlorine pesticides in vegetation samples collected in Croatia.

A pilot study was conducted to screen levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in needles of coniferous trees and in leaves, as markers of environmental pollution. Samples were collected between 1992 and 1995. Pine needles (17 samples) were collected from three sites in the Adriatic area (south face of the mountain Velebit, Križisce and island Krk) and three sites in the inland area (Zagreb, mountain Medvednica and Ogulin). PCBs, DDD, DDE, HCB, alpha-HCH and gamma-HCH were detected in all samples and their concentrations ranged from 0.02 to 22.0 ng/g dry weight. The frequency of p,p'-DDT, o,p'-DDT and beta-HCH was slightly lower and their concentrations ranged up to 3.2. Concentrations seem to vary according the sampling year. Fifteen samples from fir, spruce, larch, thuja, and from lime were all collected in Ogulin; the OCPs and PCBs levels were within the range in pine needles, but the distribution pattern depended on the species. Judging from the ratios DDE/DDT and alpha-HCH/gamma-HCH it seems that no input of DDT occurred during or recently before the sampling, while it seems that gamma-HCH (lindane) was released into the environment.

Ecosystem respiration in a young ponderosa pine plantation in the Sierra Nevada Mountains, California.

We estimated total ecosystem respiration from a ponderosa pine (Pinus ponderosa Dougl. ex Laws.) plantation in the Sierra Nevada Mountains near Georgetown, California, from June to October, 1998. We apportioned ecosystem respiration among heterotrophic, root, stem and foliage based on relationships for each component that considered microclimate and vegetation characteristics. We measured each respiration component at selected sampling points, and scaled the measurements up to the ecosystem based on modeled relationships. Over the study period, total mean ecosystem respiration was 5.7 +/- 1.3 mumol m-2 s-1 (based on daily mean), comprising about 67% from soil-surface CO2 efflux, 10% from stem and branch respiration and 23% from foliage respiration. Shrub leaves contributed about 24% to total foliage respiration, and current-year needles (1998 age class) accounted for 40% of total tree needle respiration. Root respiration accounted for 47% of soil-surface CO2 efflux. We conclude that ecosystem respiration can be estimated based on daily mean air and soil temperatures through exponential relationships with r2 values of 0.85 and 0.87, respectively. When based on both air and soil temperatures, about 91% of the variation in total ecosystem respiration could be explained by a linear regression.

Co‐occurrence of the ascomycete Lophodermium piceae and the rust fungus Chrysomyxa abietis in Norway spruce needles

The frequency of needles and the proportion of needle segments infected by Lophodermium piceae were compared in symptomless and Chrysomyxa abietis‐infected, 1‐year‐old needles of Picea abies. In late spring, symptomless needles from both rust‐infected and healthy saplings were sampled. In addition, rust‐infected, totally chlorotic needles and needles with chlorosis along about half their length from the diseased trees were examined. In all three stands, the proportion of segments infected by L. piceae was larger in the rust‐infected half of the needle than in the symptomless half; but the difference was statistically significant in only one of the stands. The proportion of L. piceae‐infected segments among the nonrust‐infected needles was the same as that found for the uninfected half of rust‐infected needles (after correction for size differences). No differences in the proportion of L. piceae‐infected segments were found between the totally chlorotic, rust‐infected needles and the green needles of diseased or healthy trees.

Short-term changes in free radical scavengers and chloroplast pigments in Pinus canariensis needles as affected by mild drought stress

Summary Potted Pinus canariensis seedlings were subjected to mild drought by withholding irrigation for one week. This treatment induced a reduction in maximum stomatal conductance (50 mmol m −2 s −1 ) compared to irrigated controls (130 mmol m −2 s −1 ). Needle water potentials of non-irrigated trees were maintained at control level (-0.44 MPa). Such a mild drought is a potential oxidative stressor due to the production of active oxygen species (AOS) in illuminated chloroplasts which lack CO 2 due to stomatal closure. Photoprotective pigments (e.g. the xanthophyll cycle) may avoid this situation through light energy dissipation, and antioxidants such as ascorbic acid, tocopherols, and glutathione, may detoxify AOS. Concentrations of ascorbate, glutathione, chlorophyll, and the xanthophyll cycle carotenoids were minimal in the evening (under low light) compared to light-saturated conditions. α-Carotene was highest in the evening. These short-term changes were not affected by drought. The xanthophyll cycle pool tended to be more de-epoxidized in strongly illuminated needles of non-irrigated trees at the beginning of the experiment, but this effect was transient. The glutathione pool was more oxidized in needles of non-irrigated trees (up to 20 percnt; of total vs. 10 percnt; at control) after the xanthophyll changes took place, whereas the redox state of ascorbate remained stable.

Amelioration of Magnesium Deficiency in a Norway Spruce Stand (Picea abies) with Calcined Magnesite

Norway spruce has shown needle yellowing and defoliation symptoms on manysites of the Bohemian Forest in north central Austria since theearly 1980s. A forest amelioration experiment was set up toevaluate the response of spruce to magnesite based fertilizerswith different solubilities. Response variables were a crownvigor index, diameter growth, nutrient contents in needles,soil solution chemistry, and soil chemistry. Soil solution atfertilized plots showed an immediate response in base cationconcentrations, nitrate concentrations and pH-values.Fertilization increased the pool of exchangeable cations in theupper 15 cm of the soil and reduced levels of exchangeable Al. Themagnesium and calcium content of the needles of dominant trees wasgreatly improved. Fertilization has increased the mineralizationrate of soil organic matter. Diameter growth, as a measure of treevigor, showed a pronounced positive response with a time delay of5 years. Our results demonstratethat magnesite based fertilizers are a viable option to improvethe nutritional status of spruce forests on granitic bedrock.

Gene induction of stilbene biosynthesis in Scots pine in response to ozone treatment, wounding, and fungal infection.

The S-adenosyl-L-methionine:pinosylvin-O-methyltransferase (PMT) gene was sequenced from Scots pine (Pinus sylvestris). The open reading frame is arranged in two exons spaced by one 102-bp intron. Promoter regulatory elements such as two "CAAT" boxes and one "TATA" box were identified. Several cis-regulatory elements were recognized: stress-responsive elements (Myb-responsive elements) as well as G, H, and GC boxes. Moreover, elicitor-responsive elements (W boxes) and a sequence resembling the simian virus 40 enhancer core were found. In phloem and needles of control trees, the transcripts of stilbene synthase (STS) and PMT were hardly detectable. Increased ozone fumigation up to 0.3 microL L(-1) enhanced the transcript level of STS and PMT in needles but not in healthy phloem. Wounding, e.g. mock inoculation, of stem-phloem was characterized by a transient increase in STS and PMT transcripts, which was more pronounced in the case of fungal inoculation. Combination of fungal-challenge or mock treatment with ozone resulted in a positive interaction at 0.3 microL L(-1). Scots pine stilbene formation appeared to be induced via STS and PMT gene expression upon ozone and fungal stress as well as wounding. The broad stress-responsiveness is in agreement with the range of various cis-acting elements detected in the STS and PMT promoters.

Carbon assimilation and nitrogen in needles of fertilized and unfertilized field-grown Scots pine at natural and elevated concentrations of CO2.

Effects of elevated CO2 concentration ([CO2]) on carbon assimilation and needle biochemistry of fertilized and unfertilized 25-30-year-old Scots pine (Pinus sylvestris L.) trees were studied in a branch bag experiment set up in a naturally regenerated stand. In each tree, one branch was enclosed in a bag supplied with ambient [CO2] (360 micromol mol(-1)), a second branch was enclosed in a bag supplied with elevated [CO2] (680 micromol(-1)) and a control branch was left unbagged. The CO2 treatments were applied from April 15 to September 15, starting in 1993 for unfertilized trees and in 1994 for fertilized trees, which were treated with N in June 1994. Net photosynthesis, amount and activity of Rubisco, N, starch, C:N ratio and SLA of needles were measured during the growing season of 1995. Light-saturated net photosynthetic rates of 1-year-old and current-year shoots measured at ambient [CO2] were not affected by growth [CO2] or N fertilization. Elevated [CO2] reduced the amount and activity of Rubisco, and the relative proportion of Rubisco to soluble proteins and N in needles of unfertilized trees. Elevated [CO2] also reduced the chlorophyll concentration (fresh weight basis) of needles of unfertilized trees. Soluble protein concentration of needles was not affected by growth [CO2]. Elevated [CO2] decreased the Rubisco:chlorophyll ratio in unfertilized and fertilized trees. Starch concentration was significantly increased at elevated [CO2] only in 1-year-old needles of fertilized trees. Elevated [CO2] reduced needle N concentration on a dry weight or structural basis (dry weight minus starch) in unfertilized trees, resulting in an increase in needle C:N ratio. Fertilization had no effect on soluble protein, chlorophyll, Rubisco or N concentration of needles. The decrease in the relative proportions of Rubisco and N concentration in needles of unfertilized trees at elevated [CO2] indicates reallocation of N resources away from Rubisco to nonphotosynthetic processes in other plant parts. Acclimation occurred in a single branch exposed to high [CO2], despite the large sink of the tree. The responses of 1-year-old and current-year needles to elevation of growth [CO2] were similar.

Molybdenum at German Norway spruce sites: contents and mobility

Molybdenum plays an important role in the nitrogen turnover of ecosystems. However, very little is known about Mo availability in forest soils. We measured the oxalate-extractable Mo concentrations of acid forest soils, the Mo, nitrate, phosphate, and sulfate fluxes from the organic forest floor into the mineral soil using resin tubes and the Mo concentrations of the tree needles at 28 different Norway spruce (Picea abies (L.) Karst.) sites in southern Germany. The supply of oxalate-extractable Mo varied from 51 to 3400 g·ha-1, with the lowest values occurring in sandstone-derived soils (370 ± 212 g·ha-1; mean ± SD). Molybdenum concentrations of current-year needles were in the range of 5 to 48 ng·g-1. The Mo needle concentrations and oxalate-extractable Mo of soils did not correlate. However, Mo fluxes (6-60 g·ha-1·a-1) from the organic forest floor into the mineral soils were correlated to needle concentrations and to the NO3 fluxes. We conclude that Mo turnover within forest ecosystems is governed by Mo plant availability of mineral soils as well as by plant Mo uptake. In addition, Mo cycling strongly affects Mo distribution within soil profiles and Mo fluxes out of the organic layer.

Radionuclides in the terrestrial ecosystem near a Canadian uranium mill--Part I: Distribution and doses.

Soils, vegetation, small mammals, and birds were measured for uranium series radionuclides at three sites near the operating Key Lake uranium mill in northern Saskatchewan. Sites, impacted by windblown tailings and mill dust, had significantly higher concentrations of uranium, 226Ra, 210Pb, and 210Po in soils, litter, vegetation, tree needles and twigs, small mammals, and birds, compared to a control site. Samples were collected from both upland jackpine and black spruce bog habitats in triplicate at each site. Both habitats were similar in radionuclide accumulation. Absorbed doses averaged 0.92, 8.4, and 4.9 mGy y(-1) to small mammals and 2.0, 5.8, and 2.8 mGy y(-1) to Lincoln's sparrows at the control, tailings, and mill sites, respectively. These doses do not include doses from short-lived radon progeny. The majority of the dose increment at the tailings and mill sites was due to 226Ra, whereas it was 210Po at the control site. Thus, use of a radiation weighting factor of 20 for alpha radiation raised equivalent doses (in mSv y(-1)) by nearly a factor of 20.

Analysis of the statistic al properties of pulses in atmospheric corona discharge

The properties of the negative corona current pulses in a single point-to-plane configuration have been extensively studied by many investigators. The amplitude and the interval of these pulses are not generally constant and depend on many variables. The repetition rate and the amplitude of the pulses fluctuate in time. Since these fluctuations are subject to a certain probability distribution, the statistical processing was used for the analysis of the pulse fluctuations. The behavior of the pulses has been also investigated in a multipoint geometry configuration. The dependence of the behavior of the corona pulses on the gap lengths, the material, the shape of the point electrode, the number and separation of electrodes (in the multiple-point mode) has been investigated, too. No detailed study has been carried out up to now for this case. The attention has been devoted also to the study of the pulses on the points of live materials (needles of coniferous trees). This contribution describes recent studies of the statistical properties of the pulses for various conditions.

Photosynthesis in Norway spruce seedlings infected by the needle rust Chrysomyxa rhododendri.

Chrysomyxa rhododendri (DC.) De Bary is a needle rust with a host shift between Rhododendron sp. and Norway spruce (Picea abies (L.) Karst.), penetrating only the new developing flushes of the conifer. Because little is known about its effects on trees, we investigated several parameters related to photosynthesis in artificially infected 3-year-old Norway spruce seedlings. The potential efficiency of photosystem II (PSII; derived from chlorophyll fluorescence measurements) was reduced in infected current-year needles as soon as disease symptoms were visible, about three weeks after inoculation. Two weeks later, photosynthetic O(2) evolution (P(max)) of infected needles was less than 20% of control needles, whereas respiratory O(2) uptake (R(D)) was about three times higher than that of control needles. Nonstructural carbohydrate concentrations were about 60% of control values in all parts of the shoots of infected trees. Photosynthetic inhibition was associated with marked decreases in chlorophyll concentration and chlorophyll a/b ratio but only a small reduction in carotenoid concentration. In infected trees, P(max) of noninfected 1-year-old and 2-year-old needles was 50 and 80% higher than in the corresponding age class of needles of control trees. Estimation of potential daily net dry mass production, based on P(max), R(D), specific leaf area, carbon content and needle biomass, indicated that seedlings infected once were able to produce 60%, and those infected twice only 25%, of the dry mass of controls. We conclude that afforestation and regeneration of Norway spruce is seriously impaired in regions where seedlings are frequently attacked by Chrysomyxa.

Radar modelling of coniferous forest using a tree growth model

The use of a tree growth model to provide statistical information about the microwave scattering components of boreal-type forests (in this case, Scots pine and Norwegian spruce), as an alternative to data obtained through intensive fieldwork, is described. The total backscatter from six test stands at C- and L-band frequency for three polarization combinations (HH, VV and HV) was predicted. Differences between measured C- and L-band data from a polarimetric airborne Synthetic Aperture Radar (EMISAR) and simulated backscatter values compare favourably with previous studies, with like- and cross-polarization differences generally less than 2.5 dB. Modelled backscatter values were consistently less than those observed. A likely explanation for such a discrepancy is the unrealistic manner in which the model incorporates the spatial distribution of tree needles.

Apoplastic and total peroxidase activities in Scots pine needles at subarctic polluted sites

A gradient survey was carried out in order to compare peroxidase activity in Scots pine (Pinus sylvestris) needles in relation to distance from the industrial centre of Monchegorsk, on the Kola Peninsula in north‐western Russia. Apoplastic and total peroxidase activity and sulphur (S), nickel (Ni) and copper (Cu) content in the needles of mature trees were measured on seven plots located between 10 and 110 km from the pollution source. Peroxidase activities in both current‐ and previous‐year needles increased towards the smelters and showed a positive correlation with needle S, Cu and Ni concentrations. Total peroxidase activities showed a more obvious relationship to the pollution gradient in winter than in autumn. The element contents in the current year needles averaged 1649 ppm (S), 128 ppm (Ni) and 118 ppm (Cu) close to the smelters, 1212 ppm (S), 37 ppm (Ni) and 67 ppm (Cu) at a distance of 40 km and 831 ppm (S), 7 ppm (Ni) and 1 ppm (Cu) at the most distant sampling plot.This study showed that both the apoplastic and total peroxidase activities responded to heavy metal and sulphur pollution up to 40 km from the smelters in winter, which indicated an increased oxidative stress in this area. The harsh climate conditions and the high pollution levels may have had additive effects. However, as peroxidases are considered a general indicator of stress, it is not possible to evaluate the extent to which single pollutants contribute to this enzyme activity.